In cryptography, plaintext is the information that a sender wishes to transmit to receiver(s). Before the computer era, plaintext simply meant text in the language of the communicating parties. Since the advent of computers, the definition has been expanded to include not only the electronic representation of text, such as email and word processor documents, but also the computer representation of speech, music, pictures, videos, ATM and credit card transactions, sensor data, and so forth. Basically, any information that the communicating parties might wish to conceal from others could be classified as plaintext. The plaintext is the normal representation of the data before any action has been taken to conceal it.
The plaintext is used as input to an encryption algorithm; the output is termed ciphertext. In some systems, however, multiple layers of encryption are used, in which case the ciphertext output of one encryption algorithm becomes the plaintext input to the next.
By way of further background, in cryptography, a stream cipher is a symmetric cipher where plaintext bits are combined with a pseudorandom cipher bit stream (keystream), typically by an exclusive-or (xor) operation. In a stream cipher, the plaintext digits are encrypted one at a time, and the transformation of successive digits varies during the encryption. An alternative name is a state cipher, as the encryption of each digit is dependent on the current state. In practice, the digits are typically single bits or bytes.
Stream ciphers represent a different approach to symmetric encryption when compared to block ciphers. Block ciphers operate on large blocks of digits with a fixed, unvarying transformation. This distinction is not always clear-cut: in some modes of operation, a block cipher primitive is used in such a way that it acts effectively as a stream cipher. Stream ciphers typically execute at a higher speed than block ciphers and have lower hardware complexity. However, stream ciphers can be susceptible to security issues.
Advances in digital multimedia and communication technologies have paved the way for people around the world to acquire, utilize, and share multimedia information. In such distributed environment, the problems associated with multimedia security are becoming increasingly important. A common way to protect multimedia content is to encrypt the entire sequence using conventional cryptographic algorithms such as the Data Encryption Standard (DES), which is a cipher (a method for encrypting information) selected as an official Federal Information Processing Standard (FIPS) for the United States in 1976, and which has subsequently enjoyed widespread use internationally.
In recent years, the DES cipher has been superseded by the Advanced Encryption Standard (AES). Due to the high data rate of multimedia signal, AES requires a considerable amount of computational power, and usually is not fast enough to meet real-time delivery requirements. In order to reduce the overhead, selective encryption has been suggested. However, the security of most of the selective encryption systems is not high, and often the coding efficiency is sacrificed. Consequently, designing a robust multimedia encryption scheme, which features high level of security and low computational cost, is a challenging task.
A multiple Huffman table (MHT) method has also been proposed that combines encryption with entropy coding using multiple statistical models alternatively in a secret order. The major advantage of the proposed MHT method is the provision of relatively secure encryption while simultaneously achieving unaffected compressio, requiring almost negligible additional overhead. Nevertheless, the basic MHT method is only secure under cipher-only and known-plaintext attacks, but is vulnerable under chosen-plaintext attacks (CPAs).
In this regard, a CPA is an attack model for cryptanalysis that presumes that the attacker has the capability to choose arbitrary plaintexts to be encrypted and obtain the corresponding ciphertexts. To improve security, enhanced MHT schemes have been proposed by either inserting random bits in the generated bit stream or integrating with a stream cipher. Another proposal has suggested random rotation in partitioned bit streams, as applied to an MHT system. However, there is still room for improvement in cryptographic algorithms.
The above-described deficiencies of current designs for cryptography are merely intended to provide an overview of some of the problems of today's designs, and are not intended to be exhaustive. Other problems with the state of the art and corresponding benefits of the innovation may become further apparent upon review of the following description of various non-limiting embodiments of the innovation.